Specify the unit of Equlibrium Constant of the following reaction. $Fe^{3+} (aq) + SCN^- (aq) \rightleftharpoons Fe(SCN)^{2+} (aq)$

Question

$\begin{array}{1 1}(a)\; Lmol^{-3} \\(b)\; Lmol^{-1} \\(c)\;L \\ (d)\;mol^{-1} \end{array}$